Recent medical studies have determined that the surgical removal of atherosclerotic plaques in the carotid bifurcation region may significantly reduce the incidence of stroke. This is so for a greater than about 70% narrowing of the region for both asymptomatic and symptomatic individuals. The surgical plaque-removal technique is known as carotid endarectomy. When this procedure is performed by an experienced surgeon, that is, one performing more than about 50 procedures per year, the morbidity and mortality are approximately 5%. The most common complication of carotid endarectomy may be stroke. Accordingly, though complications are infrequent, they tend to be life altering.
The technology exists to treat stenotic lesions of the carotid bifurcation region from an endovascular approach, for example, via transarterial catheter techniques. Endovascular therapy may typically be less traumatic to the patient, and more cost effective. For endovascular treatment of carotid atherosclerotic disease (CAD) to become more widely accepted, long-term patency rates of the treated lesions and the complication rate should be as good as or better than surgical therapy.
One study evaluating endovascular treatment of CAD has been published in the medical literature as authored by J. G. Theron et al., appearing in Radiology 201, 627-636, 1996. This study determined that angioplasty followed by stenting decreased the incidence of restenosis and reduced the risk of carotid dissection when compared with angioplasty alone. The Theron article discloses endovascular treatment of carotid artery stenosis by angioplasty, and with cerebral protection provided by a balloon blocking the vessel downstream from the stenosis. Also, when the cerebral circulation fed by the vessel being treated was so protected, the incidence of stroke decreased. The method only allowed for cerebral protection during angioplasty, and not during the stenting procedure. In other words, stent placement is described, but without cerebral protection. The Thereon article and associated U.S. Pat. No. 5,423,742 to Thereon each describe a triple coaxial catheter system that enabled angioplasty with temporary carotid occlusion, aspiration of debris, and flushing of the working site.
According to the Theron approach, a guiding catheter is first positioned to extend to adjacent the stenosis, and the catheter carrying the occlusion balloon and the dilatation catheter may be guided through a central lumen of the guiding catheter in a coaxial relationship. The guiding catheter as sized for positioning in the carotid artery, had an insufficient lumen diameter relative to the size of the desired stent to allow for positioning of the stent through the guiding catheter. Consequently the cerebral protection technique could not be used at this important step of the endovascular treatment. Despite this shortcoming, the risk of embolic complication, however, was described in the Theron article as markedly reduced because preliminary angioplasty was performed with cerebral protection. Unfortunately, stent placement without protection may also cause plaque deposits to become dislodged and, thus, possibly flow downstream to the unprotected cerebrum of the patient.
While angioplasty and stent placement techniques have been developed for other blood vessels, such as the coronary arteries, for example, developments in endovascular treatment for the carotid artery have lagged. U.S. Pat. No. 5,484,412 to Pierpont, for example, is representative of developments for advanced techniques for treating stenosis of the coronary arteries. U.S. Pat. No. 5,439,446 to Barry discloses a stent delivery system. U.S. Pat. No. 5,281,200 to Corso, Jr. et al. discloses a balloon-on-a-wire assembly and an over-the-wire catheter which slidably passes over the balloon-on-a-wire assembly for predilatation, and subsequent dilatation, respectively.